On Tue, Sep 08, 2020 at 07:03:30PM +0200, Bartosz Golaszewski wrote: > On Mon, Sep 7, 2020 at 2:22 PM Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Mon, Sep 07, 2020 at 02:06:15PM +0200, Bartosz Golaszewski wrote: > > > On Mon, Sep 7, 2020 at 1:53 PM Andy Shevchenko > > > <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > > > > > > > On Mon, Sep 07, 2020 at 12:26:34PM +0200, Bartosz Golaszewski wrote: > > > > > On Mon, Sep 7, 2020 at 11:59 AM Andy Shevchenko > > > > > <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > On Fri, Sep 04, 2020 at 08:15:59PM -0700, Randy Dunlap wrote: > > > > > > > On 9/4/20 8:45 AM, Bartosz Golaszewski wrote: > > > > > > > > > > > > ... > > > > > > > > > > > > > > +GPIO Testing Driver > > > > > > > > +=================== > > > > > > > > + > > > > > > > > +The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO > > > > > > > > +chips for testing purposes. There are two ways of configuring the chips exposed > > > > > > > > +by the module. The lines can be accessed using the standard GPIO character > > > > > > > > +device interface as well as manipulated using the dedicated debugfs directory > > > > > > > > +structure. > > > > > > > > > > > > > > Could configfs be used for this instead of debugfs? > > > > > > > debugfs is ad hoc. > > > > > > > > > > > > Actually sounds like a good idea. > > > > > > > > > > > > > > > > Well, then we can go on and write an entirely new mockup driver > > > > > (ditching module params and dropping any backwards compatibility) > > > > > because we're already using debugfs for line values. > > > > > > > > > > How would we pass the device properties to configfs created GPIO chips > > > > > anyway? Devices seem to only be created using mkdir. Am I missing > > > > > something? > > > > > > > > Same way how USB composite works, no? > > > > > > > > > > OK, so create a new chip directory in configfs, configure it using > > > some defined configfs attributes and then finally instantiate it from > > > sysfs? > > > > > > Makes sense and is probably the right way to go. Now the question is: > > > is it fine to just entirely remove the previous gpio-mockup? Should we > > > keep some backwards compatibility? Should we introduce an entirely new > > > module and have a transition period before removing previous > > > gpio-mockup? > > > > > > Also: this is a testing module so to me debugfs is just fine. Is > > > configfs considered stable ABI like sysfs? > > > > Yes it is. Or at least until you fix all existing users so that if you > > do change it, no one notices it happening :) > > > > Got it. One more question: the current debugfs interface we're using > in gpio-mockup exists to allow to read current values of GPIO lines in > output mode (check how the user drives dummy lines) and to set their > simulated pull-up/pull-down resistors (what values the user reads in > input mode). > > This works like this: in /sys/kernel/debug/gpio-mockup every dummy > chip creates its own directory (e.g. > /sys/kernel/debug/gpio-mockup/gpiochip0) and inside this directory > there's an attribute per line named after the line's offset (e.g. > /sys/kernel/debug/gpio-mockup/gpiochip0/4). Writing 0 or 1 to this > attribute sets the pull resistor. Reading from it yields the current > value (0 or 1 as well). > > This is pretty non-standard so I proposed to put it in debugfs. If we > were to use configfs - is this where something like this should go? Or > rather sysfs? Is it even suitable/acceptable for sysfs? That sounds like it would work in sysfs just fine as-is, why don't you all want to use that? configfs is good for "set a bunch of attributes to different values and then do a 'create/go/work'" type action. thanks, greg k-h
